Fatigue. And Manu and Sjax coming back and throwing things off, rotation wise. Yesterday wasn't "Let TD do whatever". The Spurs had plenty of open shots, they just didn't hit any. Lots of in and out, around the rim kind of shots.
Also, for some reason, the Spurs seem to always be caught off guard by guys like Ibaka or Faried. Seems like they don't have an answer for that.